1. Field of the Invention
The present invention relates to an image forming apparatus and a translation control method.
Description of Related Art
Generally, in an image forming apparatus that forms an image by using an electrophotographic process, the surface of an image bearing member (a photoconductor drum or the like) is electrically charged to a predetermined potential, and image light exposure is performed thereto to form an electrostatic latent image on the surface. Then, the latent image on the surface of the photoconductor drum is developed by a development section by using a developer (toner), and visualized as a toner image. The toner image thus obtained is transferred onto a recording sheet conveyed to the photoconductor drum, the recording sheet carrying the toner image is conveyed to a fixing unit, and an unfixed toner image on the recording sheet is thermally fixed by the fixing unit, thereby forming an image on the recording sheet.
In an image forming apparatus, when processing a large quantity of recording sheets of the same size at a fixing unit, edge portions of the recording sheets continuously contact against the same positions on a fixing roller of the fixing unit. Therefore, there is a known problem of scratches (hereunder, referred to as “sheet edge scratches”) created along the circumference of the fixing roller at the positions that the edge portions of the recording sheets contact against, which consequently deteriorates the image quality due to the sheet edge scratches.
To solve the foregoing problem pertinent in the art, an image forming apparatus has been developed that is adapted so as to continually change the positions at which edge portions of recording sheets contact against a fixing roller by translating the fixing unit in a direction orthogonal to the conveying direction of the recording sheets (for example, see Japanese Patent Application Laid-Open No. 2006-91224).
However, according to the technology described in the aforementioned Japanese Patent Application Laid-Open No. 2006-91224, as a result of translating the fixing unit, an abrasion difference arises between parts that edge portions of the recording sheets contact against and parts that edge portions of the recording sheets do not contact against on a surface layer of a heating member (for example, a heating roller, a heating belt or the like) and a pressing member (for example, a pressing roller, a pressing belt or the like) of the fixing unit. Consequently, there has been a problem of a gloss difference in an image that is ultimately formed on a recording sheet occurring when an unfixed toner image on the recording sheet is thermally fixed by the surface layers of a heating member and a pressing member in which an abrasion difference has arisen. The gloss difference occurs, in particular, in a case where toner images of the same image or of the same image width are formed successively on recording sheets.